Heretofore, opto-electronic conversion and time division de-multiplexing have been carried out in separate stages. It is firstly necessary to convert a multiplexed optic signal to electronic form and then to de-multiplex the electronic signal. For example, European Patent Specification No. 356,302 (Etat Francais) discloses an optical wavelength de-multiplexing apparatus. A separate apparatus would be required for time division de-multiplexing of output signals from this apparatus. This is complex and expensive. Accordingly, in many cases optic signal transmission is not used where there are many nodes such as in a network, although it would otherwise be advantageous.